^What they said^. Every Marine I know that has enlisted in the last decade got out at the end of their first enlistment. Granted thats only 5 people, but 5 out of 5 tells me the AF would be a good place to serve. If you wanna be hard core check out the PJ's.
if you want to be a hardcore medic, check out pj's.
if you want to be hardcore, check out CCT